LittleBits Mixer

[4pyros]

I've been looking a little more at the littleBits website (confusing as it is), and the previous stages (at least the ones I've looked at) provide biasing for the following buffer stage - but this doesn't prevent the problem of the volume controls changing the bias of the following stages.

Thanks for taking the time to decipher their web page to at least take a look at the other modules.

 

[4pyros]

You should also bear in mind that you don't get 'rail to rail' opamps, only 'nearish to rail' ones

I know that, its just a figure of speech.

 

[4pyros]

Unfortunately the entire littleBits system is crippled by it's lack of supply voltage, and too small a number of connections between modules

Yes but it works

 

[ronsimpson]

Yes but it works

There are a number of odd things. Like the volume control on the speaker amplifier. Good thing is the amp is AC coupled.

Yes but it works

This is the bottom line. It works for this application. Not what I would have designed. But it works. Not on external audio. But it works.
Looking back it looks (not good). Back when the first "555" oscillator was designed and not knowing what the future would bring the system probably looked good.

I wish I could see what tomorrow will bring. I can see the past.

 

[Nigel Goodwin]

There are a number of odd things. Like the volume control on the speaker amplifier. Good thing is the amp is AC coupled.

It's a perfectly valid volume control, and is quite often used in mixers - however, in this case it's a further example of design with little or no understanding of what they were doing. The entire opamp stage with volume control isn't needed at all, it actually gives a negative gain of ten, and from there down to infinity, plus it's fed from a low impedance buffer - it could be more sensibly replaced with a simple pot and series resistor, saving an opamp and the bis components etc.

 

[4pyros]

It's a perfectly valid volume control, and is quite often used in mixers - however, in this case it's a further example of design with little or no understanding of what they were doing. The entire opamp stage with volume control isn't needed at all, it actually gives a negative gain of ten, and from there down to infinity, plus it's fed from a low impedance buffer - it could be more sensibly replaced with a simple pot and series resistor, saving an opamp and the bis components etc.

Yes but the speaker and amp may not be the only output on the signal line. It has a pass thru connector that could have other things hooked up to it like motors and lights or more logic stuff, so it is buffered from the signal line.

 

[tvtech]

So glad I stayed out of this one ...until now.

So brilliant to see Members sparring and all and still being friendly to each other. Love it.

Regards,
tvtech

 

[4pyros]

So glad I stayed out of this one ...until now.

So brilliant to see Members sparring and all and still being friendly to each other. Love it.

Regards,
tvtech

Oh but you did chime in at post 40
Just wish others were interested in giving there thoughts.

 

[large_ghostman]

I am just watching and getting idea's, there is obviously a market. Modules to make sound that can plug into each other, modules able to connect to other's with say light, and Led cubes and drum machines.... Very interesting, I am looking for an angle for School to add to my list of things I sell.
I didnt think of modules before, inputs to the Led cubes to make them sound to light via different avenues and not just a mic. I cant see it yet but I am sure there is something here I can use , dont get me wrong I am not money orientated but I like the whole business thing and the record keeping etc etc. Business appeals to my OCD and building stuff to sell appeals to my creative side

 

[Nigel Goodwin]

Yes but the speaker and amp may not be the only output on the signal line. It has a pass thru connector that could have other things hooked up to it like motors and lights or more logic stuff, so it is buffered from the signal line.

You've misunderstood, the buffer is fine - it's the opamp following it (which only gives negative gain anyway) that's a total waste.

 

[4pyros]

Ya seems to only be there for the volume control, but would it bring the positive only signal back to above and below 0 volts?

 

[4pyros]

OK in trying to do some basic testing to day I found a program called DSSF3 with a signal generator and an oscilloscope.
The web site is; https://www.ymec.com/products/dssf3e/
The idea is to make waveforms from the computer to send into the littlebits mic module and use the headphone out of the littlebits speaker module hooked up to the mic input of the laptop to see the waveforms on the oscilloscope program.
But I seem to have some ground loop problems and maybe some software issues.
I will keep trying to get this to work.

 

[4pyros]

OK I can look at waveforms from my sons iphone with the oscope on my laptop.
Just using the mic input and speaker output modules the system will pass sign waves. Abit distorted though.
Adding the mixer module in between I still get a shin wave but with a little more distortion and a dip one the top of the falling edge on the positive cycle.
All and all better than I thought it would be, thought it would square the wave off.
And it definitely works good enough for a kids toy.
I think I will start making some of my own modules now that I have a better understanding of what I am working with.

 

[4pyros]

Last piece to the puzzle.
The schematic for the mic input module.
Look at this mess. Love the diode on the output of the buffer opamp.

 

[Nigel Goodwin]

Ya seems to only be there for the volume control, but would it bring the positive only signal back to above and below 0 volts?

No, there's no where in the circuit at all that does that anyway, and no reason for it to do so.

 

[Nigel Goodwin]

Last piece to the puzzle.
The schematic for the mic input module.
Look at this mess. Love the diode on the output of the buffer opamp.

Nothing wrong with that - it's there for a good reason.

Presumably it's a modulator?, giving 'dalek' type effects etc. to the voice from the mike?.

 

[4pyros]

Nothing wrong with that - it's there for a good reason.

Presumably it's a modulator?, giving 'dalek' type effects etc. to the voice from the mike?.

I will have to look that up, thanks

 

[Nigel Goodwin]

I will have to look that up, thanks

If I recall correctly it's called 'ring modulation'?, although I'm not sure that's exactly what it's doing.

 

[4pyros]

OK I found this on dalek type effects, from a wiki page;

Although the exact sound-processing devices used have varied, the original 1963 effect used equalisation to boost the mid-range of the actor's voice, then subjected it to ring modulation with a 30 Hz sine wave.

This was done using transformers and diodes at the time to modulate the audio at 30Hz.
I dont think that single diode would come close to this, but sounds like a net effect I would love to try.

 

[Nigel Goodwin]

OK I found this on dalek type effects, from a wiki page;

This was done using transformers and diodes at the time to modulate the audio at 30Hz.
I dont think that single diode would come close to this, but sounds like a net effect I would love to try.

Not the single diode, the longtailed pair that the signal rectified by the diode is controlling.